1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to a method and an apparatus for allocating persistent resources.
2. Description of the Related Art
In the 4th Generation (4G) communication system, which is a next generation communication system, active research is in progress in order to provide users with services having various Qualities of Service (QoSs) using a transmission speed of about 100 Mbps. Representative 4 G communication systems include systems based on the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standards. The IEEE 802.16 systems employ Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) schemes in order to support a broadband transmission network on a physical channel.
In a broadband wireless communication system, such as an IEEE 802.16 system, a base station allocates resources to each mobile station for transmission and reception of packets containing data. The base station transmits a message (for example, a MAP message) including resource allocation Information Elements (IEs) to each mobile station through a downlink channel. The resource allocation IEs indicate results of the resource allocation, such as the location and size of the resources to be allocated, a modulation scheme, and a coding rate. The message indicating the result of resource allocation for an uplink communication and the message indicating the result of resource allocation for a downlink communication are generally configured separately from each other. An information unit necessary for one resource allocation is referred to as a resource allocation Information Element (IE).
The resource allocation is performed for resources within a predetermined range. A related resource allocation IE is transmitted in each predetermined interval, because a resource for general data packets is allocated in the every predetermined interval. However, in the case of the Voice over Internet Protocol (VoIP) service in which packets are periodically transmitted, it may cause unnecessary waste of resources to transmit a related resource allocation IE whenever each packet is transmitted. Therefore, a persistent allocation technique, which can reduce the overhead due to the transmission of a resource allocation IE by performing persistent resource allocation, is applied to services having a periodic traffic pattern and a persistent payload size, such as a VoIP service.
According to the persistent allocation technique, in the case of a downlink communication, packets are transmitted together with a resource allocation IE indicating the persistently allocated resource (a persistent resource) are transmitted only at the time of initial resource allocation. After the initial resource allocation, packets are transmitted without a resource allocation IE. The mobile station keeps on using the persistent resource until de-allocation information or allocation change information is received even if another resource allocation IE is not received. According to the persistent allocation technique, a new resource allocation IE should be transmitted for persistent allocation of a new resource when there is a change in the already allocated resources. A de-allocation of the persistent resource occurs as soon as a de-allocation information of the VoIP service is received.
In the IEEE 802.16m system, the resource allocation is classified into a non-persistent resource allocation and a persistent resource allocation. In the IEEE 802.16m system, since the resource allocation IE is transmitted through a User Specific Control Channel (USCCH), each mobile station can receive only the resource allocation IE allocated to itself. In the USCCH, it is preferred that each resource allocation IE has a persistent length, in order to enable each mobile station to easily identify the resource allocation IE allocated to itself. In designing the resource allocation IE in a wireless communication system using the persistent allocation as described above, a technology for minimizing the fields included in the resource allocation IE is needed in order to reduce the size of the resource allocation IE.